Conventional moving walkways include a chain of conveyor plates moving in a circuit for the purpose of providing a continuous movement along a specific path. The conveyor plates or steps are connected to said traction chain circuit, which chain acts moved by a drive system.
Due to the fact that the wheel moving said chain must have a minimum number of teeth to prevent speed variation problems in the walkway, the size of the head is defined by the primitive diameter of this wheel.
In the tensioning head, the chain is usually tensioned with a wheel having a number of teeth identical to that of the drive wheel or with a circular guide which must have a minimum radius to prevent the tensioner from oscillating due to the aforementioned effect.
As a result, the sizes of the heads are determined by the size of the minimum guide necessary to carry out the oscillation-free turnaround or by the primitive diameter of the turnaround wheel.
In a conventional walkway, the only way to reduce the size of these two turnaround options is the reduction of the chain pitch, but this is not cost-effective because it forces placing too many linkages in the chain. In addition, there comes a time in which the linkages cannot be sized if the pitch is very small.
The number of teeth in the drive wheel cannot be reduced without the speed fluctuating but a wheel with less teeth could be placed in the tensioning station. In this case, sinusoidal variations of the position of the tensioning wheel occur when the upper branch and the lower branch have the same speed determined by the tractor system.
If the turnaround is carried out with a circular guide, the problem is the same as when a wheel with a primitive radius equal to the radius of the turnaround curve is used. If this radius is reduced, the movement is increasingly greater like as if the number of teeth of the wheel is reduced.
In short, the dimensions of moving walkways are fixed in the drive by a minimum number of teeth and in the tensioning head by a minimum radius preventing the aforementioned effect, making it impossible to reduce the size of the walkway.
Furthermore, when the size of the turnarounds is to be reduced, it is necessary for the size of the pallets to be as small as possible to turn them around in less space and it is necessary to turn around in radii which are as small as possible. This can be achieved either with turnaround wheels of up to at least 3 teeth or with circular turnaround curves.
Due to the effects relating to the fact that the pallets do not form a continuous band, when the walkway is tensioned an oscillation occurs in the position of the tensioner, causing vibrations which are transmitted to the rest of the walkway, wear in the tensioning mechanism and noise.
This effect is greater the smaller the number of teeth of the wheel with which the turnaround is carried out or the smaller the radius of the circular curve with which the turnaround is carried out.
Methods have been proposed which provide turnaround curves for solving this problem, like that of application WO03066501. This document describes the use of a geometry eliminating the vibrations caused in the traction chain when the turnaround is carried out with a circular guide, by means of a turnaround guide formed by three sections, two of which sections are circular and have a radius equal to half the distance between the upper branch and the lower branch of the straight part of the stairs and the other of which is defined by the two previous sections when the speed of the lower branch and the upper branch are constant.
This method causes, in certain combinations of chain pitch and distances between branches, that the first derivative of the path is not the same when it approaches a control point at each of its two ends. This causes the guiding path to not be smooth enough, giving rise to low-quality rolling as well as excessive wear of the guiding rollers.
When turnarounds are carried out on very few rollers rolling on a guide, there is the problem that upon tensioning, said tension rests on very few rollers and there is the risk of loading them excessively. For some combinations of chain pitch and walkway height, the method proposed in WO03066501 determines a not very vertical contact at the time when only two rollers are on the turnaround guide, causing the tension to which each roller is subjected to be very high, such rollers being able to be damaged, as can be seen in FIG. 1.
In addition, this patent proposes the use of said guide for mechanical stairs. The size of each of the steps of the stairs has a minimum size which is fixed by the height of the turnaround heads. It is not possible to reduce the size of the stairs by means of using this turnaround curve.